The growing emphasis in recent years on measures to deal with water pollution problems has led to a substantial displacement of starch as the previously established standard cotton textile sizing material because of its inordinately high biological or biochemical oxygen demand value (BOD). In addition, the greatly increasing use of polyester fibers, either in blends with cotton or by itself, in the manufacture of textile fabrics has made it more difficult to obtain adequate adhesion with a starch size.
A notable alternative sizing material providing significant advantage in dealing with both of these problems is polyvinyl alcohol, which has a much reduced BOD value as well as adhering well to polyester. However, the chemical oxygen demand (COD) of polyvinyl alcohol is still appreciable and currently proposed anti-pollution standards make it necessary to avoid stream or sewer dumping of effluent from desizing operations where this alternative sizing material or others of the same sort, such as carboxymethycellulose, are used just as fully as when starch is used for sizing.
The present invention provides for handling desizing effluent in compliance with the anti-pollution standards now in prospect in a practical manner which allows advantageous recovery of the sizing material for reuse and recycling of the remaining effluent for desizing purposes.